UnevenArthur Thomas, Gemstones (2009) Tough, UnevenArthur Thomas, Gemstones (2009) Tough, Brittle, Uneven
Subconchoidal, Uneven, Conchoidal, Uneven
Mn 8Si 6O 15(OH,Cl) 10Ulrich Henn and Claudio C.
Mn2+ Al(PO 4)(OH) 2H 2OMichael OâDonoghue , Gems, Sixth Edition (2006)